Comment by nine_k
6 hours ago
Imagine that you're a highly intellectual, highly technical, and highly responsible person in control of large sums of governmental or corporate money. You don't want to waste the money, you want stellar results (in spacecraft industry, maybe literally so).
Would you assign a large sum of money to a group that cannot present their design clearly, neatly, and concisely? If they are struggling even with that, would you trust them to be good at actually designing a spacecraft soundly, economically, and in a reasonable time?
"If you can't explain it to a five-years-old, you likely do not understand it yourself", said one of the greatest modern scientists, who also was notoriously good at explaining things.
What often happens next is, another party comes up in the middle to manage the interaction between both of you (with the proper bump in the ask price), because there's not only so many decision makers looking for neat presentations and whatnot but also there's only so many teams willing to do the actual work.
I think that Feynman was talking about preparing a freshman-level lecture for Caltech-standard freshmen, but maybe you have somebody else in mind.
I would say: You either don't understand your subject, or don't understand your audience, if you can't explain your subject to your audience, at the highest level they can understand, coherently.
The average person can understand anything ... at some level. Being able to match that level is positive evidence (but not proof) of competence.
I think if you understand something really well (anything: the law of gravity, the Curry-Howard isomorphism, electrolytic dissociation, general relativity,...), you can find a bunch of comparisons, or metaphors, or other ways to explain it so that an interested five-years-old will get a rough idea. A very rough idea indeed, but one that could allow them to ask qualitatively reasonable questions, and that forms an intuition which helps during a real study.